In recent years mobile operators have started to offer mobile wireless broadband communication service based on Third Generation Partnership Project (3GPP), e.g., Wideband Code Division Multiple Access (WCDMA). Further, fuelled by new devices designed for data applications, the end user performance requirements are steadily increasing. Moreover, the increased demand for mobile broadband service has resulted in traffic volumes being handled by high speed packet access (HSPA) enabled WCDMA networks.
Enhanced Uplink (EUL) was introduced in the 3GPP Rel-6 standard to improve HSPA performance. Since the uplink transmission from a wireless device to a base station is, by design, non-orthogonal, fast closed-loop power control is necessary to address the near-far problem, where a wireless device captures a strong signal from a nearby source, making it difficult to receive a weak signal from a source located further away. The base station, which may be referred to as a node B (NB) in a WCDMA network, measures the received signal-to-interference ratio (SIR) and sends power control commands in the downlink transmission from the NB to the wireless device e.g., user equipment (UE), to adjust the transmission power. Power control commands can be transmitted using a dedicated physical channel (DPCH) or, to save channelization codes, the fractional dedicated physical channel (F-DPCH). The non-orthogonality between wireless devices causes interference leakage between the wireless devices. As a result, the uplink throughput is often limited to 2-3 megabits per second (Mbps) in scenarios with multiple wireless devices.
To enable high-bitrate operation in a real-network environment it is necessary to isolate wireless devices using high-bitrate or high receive power from wireless devices that are vulnerable to the high interference created by the high-bitrate wireless devices, e.g., wireless devices engaged in voice communications, which require considerably lower receive power at the base station. One way to accomplish this within the current HSPA technology is to make use of a “clean carrier” concept. Briefly, in this concept, carriers are divided into regular carriers and clean carriers. The regular carriers provide the basic needs of a wireless device. The clean carriers are dedicated exclusively to high-bitrate transmissions. On a clean carrier, wireless devices are scheduled by the network to transmit one at a time by Time Division Multiplexing (TDM), as much as possible in order to avoid interfering with one another.
There are different methods for accomplishing this within the current, pre Rel-12 3GPP standard. One method is to make use of the Inter-Frequency Handover (IFHO) procedure and another method is to make use of the 3GPP Rel-9 Dual-Carrier high speed uplink packet access (HSUPA) feature (also known as Dual Cell enhanced dedicated channel (E-DCH) operation). In the 3GPP Rel-12 standard work item, in further enhanced uplink (EUL) enhancements, current various uplink improvements which can improve the HSPA performance are standardized. One of the sub-topics being discussed by the 3GPP standards entities is to enable high user bitrates in single and multi-carrier uplink mixed-traffic scenarios via enhancements to the existing Rel-7 continuous packet connectivity (CPC) and Rel-9 Dual-Carrier HSUPA features for a more efficient “clean carrier” operation.
In terms of power control, in the current CPC base line algorithm, whenever there is an interruption in the transmission, the power of the DPCCH is derived from the previous value that was used in the last slot before the transmission gap on the corresponding carrier. While the current standardized solution can be a good approach when the wireless device is dealing with short gaps, it can be highly inaccurate when dealing with long inactivity periods, since in those cases the channel would be completely uncorrelated. Since the channel could be completely uncorrelated between the transmissions when using the longest values defined for the current wireless device discontinuous transmission (DTX) cycle of 2 lengths (i.e., 32, 40, 64, 80, 128, 160 subframes), inheriting power from the previous transmission would require a longer re-establishment time for proper inner-loop power control.
Thus, while the power control according to the current standard can be effective for short gaps, the channel quickly gets uncorrelated after longer DTX periods, leading to longer re-establishment time for proper inner-loop power control.